This application is based upon, claims the benefit of priority of, and incorporates by reference, the contents of Japanese Patent Application No. 2002-318836 filed Oct. 31, 2002.
1. Field of the Invention
The present invention relates to a valve timing adjustment device for an internal combustion engine (hereinafter, xe2x80x9cenginexe2x80x9d) for adjusting the timing (hereinafter, xe2x80x9cvalve timingxe2x80x9d) of at least one of an air intake valve and an exhaust valve.
2. Description of the Related Art
A conventional technique is known in which a valve timing adjustment device is provided to a transmission system for transmitting drive torque from a drive shaft (i.e., crankshaft) of an engine to a driven shaft (i.e., camshaft), to open and close an air intake valve and an exhaust valve of the engine, where the valve timing adjustment device adjusts the timing of the valves. According to the conventional technique, the valve timing adjustment device varies the rotational phase (below, simply xe2x80x9cphasexe2x80x9d) of the camshaft with respect to the crankshaft. Varying the phase in this way adjusts the valve timing, which may improve engine power output, fuel consumption, etc.
Patent Document 1 (Japanese Patent Publication No. 2001-41013) recites one example of a valve timing adjustment device. The recited device has a first rotor rotated by means of the camshaft drive torque, and a second rotor that rotates together with the camshaft in the same direction as the first rotor. In this configuration, the second rotor is rotated relative to the first rotor to vary the camshaft phase with respect to the crankshaft.
According to the valve timing adjustment device recited in Patent Document 1, a moveable operating member is moved along a radial direction of the first rotor and the second rotor, and a link is used to convert the radial movement of the moveable operating member into rotational movements by the two rotors as relative to each other. According to this construction, the degree of phase shift by the second rotor with respect to the first rotor (and, therefore, the degree of phase shift by the camshaft with respect to the crankshaft) is dependent upon the length of the arm constituting the link. However, the length of this link, which enables the conversion of the movement, is limited. As a result, the degree of phase shift possible by the camshaft with respect to the crankshaft is also limited.
An object of the present invention is to provide a valve timing adjustment device that enables a great degree of freedom when setting the phase shift of a driven shaft with respect to a drive shaft.
According to a first aspect of a valve timing adjustment device of the present invention, a first hole in a first rotor forms a first track extending so as to vary its radial distance from a center rotation line, and the first hole makes contact with a control member passing through the first track, with the contact occurring on the two sides of the first hole toward which the first rotor rotates. Further, a second hole in a second rotor forms a second track extending so as to vary its radial distance from a center rotation line, and the second hole makes contact with the control member passing through the second track, with the contact occurring on the two sides of the second hole toward which the second rotor rotates. In addition, the first track and the second track slant toward each other in the rotational directions of the first rotor and the second rotor. Therefore, when the control means acts to change the control member""s radial distance from the rotation centerline, the control member presses against at least one of the first hole and the second hole, whereby the control member passes through both the first track and the second track, and thus the second rotor is caused to rotate relative to the first rotor.
In the valve timing control device which operates in the foregoing manner, the degree of phase shift of the second rotor with respect to the first rotor is dependent upon the length of the first track and the second track and the degree to which the first track and the second track slant toward each other. By extending the first track and the second track such that they vary their radial distances from the rotation centerline, relative freedom is achieved in determining the length and the mutual slant of the tracks. In turn, this increases freedom in setting the degree of phase shift of the second rotor with respect to the first rotor, and therefore, the degree of phase shift of the driven shaft with respect to the drive shaft.
Note, however, that the mutually slanting first track and second track may be formed to intersect each other, or may also be formed in such that they do not intersect each other. According to a second aspect of the valve timing adjustment device of the present invention, the first rotor and the second rotor each have a plurality of pairs of the first hole and the second hole, arranged along the direction of rotation, such that each pair corresponds separately to each of a plurality of control members. Such a configuration alleviates unbalanced weight distribution around the rotation centerline.
According to a third aspect of the above-mentioned valve timing adjustment device of the present invention, an energizing means energizes one of the first rotor and the second rotor so as to advance that one rotor toward its direction of rotation, and energizes the other rotor so as to retard its movement toward its direction of rotation. A first wall portion formed to either the first rotor or the second rotor forms a first track extending so as to vary its radial distance from the rotation centerline, and the first wall portion makes contact with the control member passing through the first track in such a way that the contact occurs on the retardation side in terms of that rotor""s direction of rotation.
Further, a second wall portion formed to the other rotor forms a second track extending so as to vary its radial distance from the rotation centerline, with the second wall making contact with the control member passing through the second track in such a way that the contact occurs on the advancement side in terms of the second rotor""s direction of rotation. Here, the first track and the second track slant toward each other along the directions of rotation of the first rotor and the second rotor. Therefore, when the control means varies the control member""s radial distance from the rotation centerline, the following operations occur in accordance with the direction in which the radial distance is being changed.
First, the energizing means causes the first wall portions and the second wall portions to be pressed against the control members, whereby the control members are caused to pass through the first track and the second track, and the second rotor is caused to rotate toward the advancement side or toward the retardation side relative to the first rotor. Second, at least one of the first wall portion and the second wall portion is pressed by the control member, whereby the control member is caused to pass through the first track and the second track, and the second rotor is caused to rotate toward the advancement side or toward the retardation side relative to the first rotor.
In the valve timing adjustment device operating in the foregoing manner, the degree of phase shift of the second rotor with respect to the first rotor is dependent upon the length of the first track and the second track and the degree to which the first track and the second track slant toward each other. By extending the first track and the second track such that each track varies its radial distance from the rotation centerline, relative freedom is achieved for setting the length and the mutual slant of the two tracks. In turn, this increases the degree of freedom in setting the degree of the phase shift of the second rotor with respect to the first rotor, and therefore, the degree of the phase shift of the driven shaft with respect to the drive shaft. Note, however, that the first track and the second track, which slant toward each other, may be configured such that they intersect with each other, or may be configured such that they do not intersect with each other.
According to a fourth aspect of the valve timing adjustment device of the present invention, it is further desirable that the first rotor and the second rotor have a plurality of pairs of the first wall portion and the second wall portion arranged along the rotational direction of the rotor, with each of the pairs of wall portions corresponding individually to each of a plurality of control members. Such a construction alleviates unbalanced weight distribution around the rotation centerline.
According to a fifth aspect of the valve timing adjustment device of the present invention, the first track and the second track are formed as straight lines. This configuration facilitates working on the holes and the wall portions forming the two tracks.
According to a sixth and a seventh aspect of the present invention, the first track and the second track are formed as curved lines. This configuration facilitates setting the correlation between the control members"" radial distance from the rotation centerline, and the rotational phase of the second rotor with respect to the first rotor (e.g., a simple proportional relationship can be taken advantage of).
According to an eighth aspect of the valve timing adjustment device of the present invention, the first track and the second track intersect each other at places determined by the rotational phase of the second rotor with respect to the first rotor, and the bar-shaped control member passes through the point of intersection between the first track and the second track. This configuration is a simplified construction.
According to a ninth aspect of the present invention, the control member has individual rolling elements at the point where it makes contact with the first rotor and at the point where it makes contact with the second rotor. Because of this configuration, when the control member reverses the direction in which its radial distance from the rotation centerline is being changed, the second rotor can smoothly change its direction of rotation with respect to the first rotor.
According to a tenth aspect of the valve timing adjustment device of the present invention, the control holes in the control rotor form control tracks extending at a slant with respect to the radial axis line, so as to vary their radial distance from the rotation centerline, with the control holes making contact with the control member passing through the control hole. This contact occurs on both the radially inward side and the radially outward side of the control hole. Therefore, when the torque application means applies the advancement side torque or the retardation side torque to the control rotor, and the control rotor rotates relative to the first rotor to pass through the control track, the control hole presses against the control member, thus varying the radial distance of the control member from the rotation centerline.
According to an eleventh aspect of the valve timing adjustment device of the present invention, supplementary energizing means energizes the control member in one direction along the radius of the control rotor. Furthermore, the control holes in the control rotor form the control tracks extending at a slant with respect to the rotation centerline so as to vary their radial distance from the rotation centerline, with the control hole making contact with the control member passing through the control track, and with this contact occurring on either the radially inward side or the radially outward side of the control hole. Therefore, when the torque application means applies either the advancement side torque or the retardation side torque onto the control rotor, and the control rotor rotates relative to the first rotor, the control member is pressed by the supplementary energizing means toward the control wall portion, and thus passes through the control track, thereby changing the radial distance of the control member from the rotation centerline. Moreover, when the torque application means applies the opposite torque to the control rotor, and the control rotor rotates relative to the first rotor, the control member receives pressure from the control wall portion and thus passes through the control track, thereby changing the radial distance of the control member from the rotation centerline.
According to a twelfth aspect of the valve timing adjustment device of the present invention, the control track is formed as an arc arranged off-center from the rotation centerline. This configuration reduces the couple of forces bearing on the control member due to the action force of the first rotor, the second rotor, and the control rotor.
According to a thirteenth aspect of the valve timing adjustment device of the present invention, the control track is formed in a spiraling pattern. This configuration decreases the couple of forces bearing on the control member due to the action force of the first rotor, the second rotor, and the control rotor.
According to a fourteenth aspect of the valve timing adjustment device of the invention, the control track is formed as a straight line. This configuration facilitates working on the control hole and the control wall portion forming the control track.
According to a fifteenth aspect of the valve timing adjustment device, the ends of the control track are formed roughly at right angles with respect to the radial axis line of the control rotor. This configuration decreases the rate of change of the control member""s radial distance from the rotation centerline as it passes through to the end of the control track. This prevents the control member from having to make a forceful collision with the control hole or the control wall portion at the ends of the control path. As a result, loud noise, damage and the like caused by such collisions can be prevented.
According to a sixteenth aspect of the valve timing adjustment device, the control means is provided with a holding means which maintains the rotational position of the control rotor with respect to the first rotor, at a time when the torque application means is not applying torque to the control rotor. This configuration enables the rotational phase of the control rotor with respect to the first rotor to be maintained at a desired phase without depending on the torque application means, at times such as immediately after the engine is started, or when the engine is off. Moreover, by maintaining the rotational phase of the first rotor, the rotational phase of the driven shaft with respect to the drive shaft can also be maintained as desired.
According to a seventeenth aspect of the valve timing adjustment device, the torque application means has an electric motor for generating the torque applied to the control rotor. This configuration simplifies construction of the torque application means and guarantees generation of the torque to be applied to the control rotor.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.